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AndroidOperating system · Google

CVE-2021-39796

HIGH · 7.3 CVSS v3.1 Published 2022-04-12
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
73/100
Remediation priority · Elevated

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
In HarmfulAppWarningActivity of HarmfulAppWarningActivity.java, there is a possible way to trick victim to install harmful app due to a tapjacking/overlay attack. This could lead to local escalation of privilege with User execution privileges needed. User interaction is needed for exploitation.Product: AndroidVersions: Android-10 Android-11 Android-12 Android-12LAndroid ID: A-205595291

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

The HarmfulAppWarningActivity in Android lacks proper protection against tapjacking/overlay attacks, allowing a malicious application to draw an overlay on top of the system's warning dialog. This can trick users into unknowingly granting permissions or installing harmful applications by intercepting or redirecting touch events.

MitigationImplement touch validation and overlay detection protections in HarmfulAppWarningActivity, such as using FLAG_SECURE to prevent screenshots and adding mechanisms to detect when another window may be overlaying the activity.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
AndroidOperating system
Affected:= 10.0= 11.0= 12.0= 12.1

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Local
Complexity
Low
Privileges
Low
User interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify Android version
    Go to Settings > About Phone > Android version (or run 'getprop ro.build.version.release' via ADB)
    Affected if The version is 10.0, 11.0, 12.0, or 12.1 exactly
  2. Check for overlay permission status
    Go to Settings > Apps > Special app access > Display over other apps (or run 'appops get <package> SYSTEM_ALERT_WINDOW' via ADB shell)
    Affected if Any untrusted application has SYSTEM_ALERT_WINDOW permission granted, enabling overlay capabilities
  3. Verify if HarmfulAppWarningActivity is accessible
    Use a tool like 'dumpsys package com.android.phone' (or relevant package) via ADB to check if the activity is exported and accessible to other apps
    Affected if The activity is exported without proper protection measures (FLAG_SECURE not set)
  4. Inspect installed apps for overlay capabilities
    Review installed applications in Settings > Apps and note any that have 'Display over other apps' permission granted to unknown or untrusted sources
    Affected if Apps with overlay permissions are installed from unknown sources on an affected Android version

A user is affected if their device runs Android 10.0, 11.0, 12.0, or 12.1 AND has any application with SYSTEM_ALERT_WINDOW (overlay) permission from an untrusted source.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Implement touch validation and overlay detection protections in HarmfulAppWarningActivity, such as using FLAG_SECURE to prevent screenshots and adding mechanisms to detect when another window may be overlaying the activity.

Recommended fix High confidence

Android 13 (or December 2021 security patch level and above for Android 10/11/12/12.1)

  1. Check current Android version and security patch level in Settings > About Phone > Android version
  2. If running Android 10, 11, 12, or 12.1, check for system updates in Settings > System > Software Update
  3. Apply the December 2021 security patch update or later if available for your device
  4. If no update is available from your device manufacturer, consider upgrading to Android 13 which contains the fix
  5. Alternatively, avoid installing apps from untrusted sources and exercise caution with any app installation prompts to mitigate the tapjacking risk until the patch can be applied
Caveat Minimal; security patch updates typically have no breaking changes. If upgrading major Android versions (e.g., 12 to 13), review app compatibility.

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Android Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing4.0 h
  • Review / QA2.0 h
12.0 hours of engineering $2,080
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-39796 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data